Coating compositions and methods of coating metal products



nited States Patent COATING COMPOSITIONS AND METHODS OF COATING METALPRODUCTS Wesley J. Wojtowicz, Detroit, -Mich., assignor to The H. A.Montgomery Company, a corporation of Michigan No Drawing. ApplicationMarch 5, 1952, Serial No. 275,030

7 Claims. (Cl. 29-424) This invention relates to coating compositionsand methods of coating metal products for cold working, for example bydeep drawing, shearing, form rolling and the like.

Before a metal workpiece can be worked, it is usually necessary tolubricate its surface. Whenever a lustrous surface is sought in thefinished product, itis desirable to finish the surface prior to the.cold working operation. Protective coating materials are known whichwhen used in conjunction with a lubricant rendera finished surfacemar-proof during the working operation. Howevenmost of the mar-proofcoatings with which I amfamiliar have disadvantages, such as causingcoated workpiecesto stick together (blocking effect) or being corrosiveto some metals. It would be desirable to apply the mar-proof coatingmaterial to the metal as the latter is finished in a continuous strip orsheet mill, but the foregoing disadvantages have prevented thispractice.

An object of the present invention is to provide improved methods ofpreparing 'metalproducts for cold working in which the metal surfacescan be finished to a suitable luster and coated, the coated product canbe coiled or stacked without the contacting surfaces sticking together,and subsequently the product can be cold worked with the coatingprotecting its surfaces against marring.

A further object is to provide improved coating compositions whicheifectively protect metal surfaces against marring during cold working,possess good adhesion to metal surfaces, show no tackiness or blockingeffect, and are nonhygroscopic, noncorrosive, impervious to ordinarylubricants, yet are easily removed from a workpiece after the latter hasbeen cold worked.

Further objects are to provide coating compositions which have theforegoing improved properties and can be applied to continuous lengthsof metal in a strip or sheet mill, and to provide coatingmethods whereinthe metal is coated in the strip or sheet mill, whereby the metal can bedelivered in coiled or stacked form to a fabricator already coated forsubsequent working.

A further object is to provide as an improved article of manufacture ametal product coated with a composition which protects it during coldworking and yet is not tacky.

Coating compositions of the present invention consist essentially ofdewaxed shellac dispersed by. means of an alkali in aqueous glycol. Theycontain suflicient volatile alkali to neutralize the shellac, andadvantageously can contain a wetting agent and a dye. The basicformulation by weight is as'fol-lows:

Dewaxed shellac .10 to 1.8.percent. Glycol to 25 percent of the weightof dewaxed. shellac. Volatile alkali "sufficient to new .tralize. theacidity ofthesshellac.

ous alkaline solutions.

Wetting agent 0 to 0.5 percent. Dye 0 to 0.04.percent. Water remainder.

KOH necessary to neutralize 1 gr.) and is thermoplastic,

having a tack point of about 205 F. When simply heated to 400 F. for2-hours, dewaxed shellac undergoes a molecular rearrangement whereby itsacid number drops to about 50 and it becomes tack-free at 250 F., but itremains thermoplastic. When dewaxed shellac is similarly heated in thepresence of a suitable glycol, the acid numberdrops to about 15 and onprolonged heating the product becomes thermosetting. This reactionproduct forms the basis of the coating material used in the presentinvention, but, because of difficulties in obtaining a suitable solvent,I prefer to apply these ingredients 'to the workpiece in unreacted formand to produce .a

thermosetting coating .film .by subsequent heating. Shellac is used inthe dispersion in an amount of l0:to 18 *percent by weight, sincegreater concentrations become shellac content with certain natural orsynthetic resins.

Such resins should have an acid number of at least and arefurthercharacterized by their solubility in aque- Examples of suitableresins are Manilla- DEB, a natural resin, "Ambero1 750, manufacturedby.Rohm and Haas, and Arochem 450, manufactured by U. S. IndustrialChemicals, Inc. I prefer the straight shellac, but in the event of ascarcity, such replacement extends the, supply.

The glycols I have found particularly useful for the present inventionare ethylene glycol, hexylene glycol and glycerin. They are usedin anamount equal to about 5 to 25 percent of the weight of dewaxed shellac..Coatings produced with lessthan 5 percent glycol tend tobe brittle,whilethose produced with more than 25 percent tend to be tacky. Theoptimum proportion varies slightly with different glycols, being about20 percent for hexylene glycol and 15 percentfor ethylene glycol andglycerin.

The volatile alkali canbe ammonia or morpholine or other equivalents. Itis used in an amount sufiicient to neutralize the :acid content of thedewaxed shellac, preferably with a'reasonable excess. The alkali isremoved when the coating is heated, so that the exact amount of excessis not critical. About 2.0 to 3.6 percent bywei'ght of the solutioneither ofammonium hydroxide (28 percent NHs) or morpholine furnishessatisfactory results.

The wetting agent used optionally conveniently can be Aerosol GT orother known equivalents for increasing the wetting action of thesolution .on metal surfaces. The dye also used optionally convenientlycan be basic fuchsine and furnishes a ready indication as to whenthecoating is cured properly, as hereinafter explained.

The preferred procedure in making up compositions .of the presentinvention is ,first to grind the dewaxedshellac and disperse it in'water andvolatilealkali at a temper- .ature of about F. After theshellacziszcompletely .troduced.

ireceived sufficient heating.

heating step and allowing it to cool slowly in air. coiled strip retainsits heat long enough to accomplish the necessary cure.

Specific examples of compositions contemplated by the present inventionfollow. In each example the proportions are by weight.

Example I Percent Dewaxed shellac 13.0 Hexylene glycol 2.6 Morpholine2.7 Aerosol OT (25% aqueous) 2.0 Water 79.7

Example ll Percent Dewaxed shellac 18.0 Ethylene glycol 2.7 Ammoniumhydroxide (28% NHs) 3.6 Aerosol OT (25% aqueous) 2.0

Water 73 .7

Example 111 Coating compositions of the present invention are applied tothe surface of a metal workpiece after the surface has been cleanedthoroughly. The workpiece can be of various metals, such as plain carbonsteel, stainless or other alloy steel, aluminum, magnesium and numerousothers. If desired, the surface can be polished to a high luster whilethe workpiece still is fiat before the coating is applied. Any usualprocedure can be employed for applying the coating. For example, I haveapplied coatings successfully by dipping, spraying, spreading thecomposition with a roller or knife, and by flowing the composition overthe metal.

After receiving its coating, the workpiece is heated to dry and set thecoating. Preferably the heating is performed at 350 to 400 F. for abouta half minute to a minute, although temperatures up to 450 F. can beused but are not preferred since the resulting coating is more ditlicultto remove. Equivalent results can also be obtained by heating to lowertemperatures for longer intervals, for example, by heating to 300 forabout 10 minutes. A dye incorporated in the composition furnishes aconvenient means for indicating when the coating has In the example ofbasic fuchsine dye, the coating is blue as deposited. On heating the dyedecomposes and becomes successively green, golden and brown. The coatingshould be heated until the coating attains a golden or a brown color.After this initial heating, the workpieces are cured by holding them ata temperature of 200 to 300 F. for about two hours. When the coating isapplied to strip material, it can be cured simply by coiling the stripimmediately after the The Coatings applied in accordance with thepresent invention, after curing are exceeding thin.

4 Their thickness should be within the range of 20 to millionths of aninch.

After the coating has been cured, the workpiece can be cold worked inany desired way, such as deep drawing, shearing, form rolling and thelike. The coating is nonlubricating so that for more diflicultoperations a lubricant should be supplied. The coating is impervious toall the common lubricants of which I am aware so that any standardlubricant can be used for this purpose. The coating effectively protectsthe surface of the workpiece against marring, so that if this surfacehas been polished it retains its lustre even after severe working and isfree of scratches or mars. For shearing workpieces, which I define asincluding blanking, piercing, cutting and perforating, the coatings havespecial value in their ability to protect the dies.

After the cold working operation, the coating can be removed eithermechanically by bufling or chemically by dissolving the coating materialin an alkaline solution. Any of the commercial balanced industrialalkali cleaners at concentrations of about 4 ounces per gallon appearsuitable. For example, I have used successfully a cleaner which consistsby weight of the following:

Caustic soda percent 20 Water glass do 15 Trisodium phosphate do 15Rosin soap do 10 Sodium carbonate balance The workpiece is immersed inthe cleaner solution for about 2 minutes at B, after which the coatingeasily is removed with a water spray.

From the foregoing description it is seen that the present inventionfurnishes coating compositions which effectively protect metal surfacesduring cold working and at the same time do not have the undesirableproperties of being corrosive or hygroscopic or exhibiting or blockingeffect. According to the cold working method of the invention, thecoating can be applied well in advance of the working operation and theworkpiece first can be polished to a high luster. Very conveniently thecoating can be applied to metal strip in a finishing mill and the stripcan be heated and then coiled all in a continuous operation.

While I have described only certain preferred embodiments of theinvention, it is apparent other alternatives may arise. Therefore I donot wish to be limited by the disclosure, but only by the scope andobvious equivalents of the appended claims.

I claim:

1. A method of cold Working a metal workpiece comprising cleaning andfinishing the surface of a workpiece, applying to the surface a singlecoating which has a thickness of 20 to 150 millionths of an inch and isof a thermosetting composition consisting by weight of the following:

dewaxed shellac 10 to 18 percent,

glycol 5 to 25 percent of the weight of dewaxed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellac,

Water remainder,

the glycol being of the class which consist of hexylene glycol, ethyleneglycol and glycerin, said composition being in the form of an unreactedaqueous dispersion when it is applied to the surface of the workpiece,heating the coated surface to a temperature of 350 to 450 F. for a halfminute to a minute to dry and set the coating, curing the resultingthermally set coating by retaining this surface at a temperature of 200to 300 F. for about two hours, cold working the coated workpiece withthe coating protecting its surface against marring, and removing thecoating by washing with a water solution of a balanced industrial alkalicleaner.

2. A method as defined in claim 1 in which the coating is applied to theworkpiece while the latter is in continuous strip form, and the coa ingis cured by coiling the strip immediately after the first heating step,the contacting coated surfaces remaining free of cohesion for subsequentuncoiling.

3. A method of preparing a thermosetting coating composition which isadapted to be applied to metal products to enable them to be cold workedcomprising dispersing ground dewaxed shellac in water and volatilealkali at a temperature of about 175 F., the resultant dispersioncontaining about 10 to 18 percent by weight of dewaxed shellac andsufiicient alkali to neutralize the acidity of said shellac, and addingto said dispersion at said temperature a glycol of the group consistingof hexylene glycol, ethylene glycol and glycerin, the glycol beingpresent in an amount equivalent to 5 to 25 percent of the weight ofdeWaXed shellac, said dewaxed shellac and said glycol remainingunreacted in said dispersion but forming a thermosetting coating whenapplied to the surface of a workpiece, dried and heated at 350 to 450 F.for about half a minute to a minute.

4. A method of preparing metal products for cold working comprisingcoating the surface thereof with a thermosetting composition whichconsists by weight of the following:

dewaxed shellac to 18 percent glycol 5 to 25 percent of the weight ofdewaxed shellac volatile alkali sufricient to neutralize the acidity ofthe shellac water remainder,

the glycol being of the group which consists of hexylene glycol,ethylene glycol and glycerin, said composition being in the form of anunreacted aqueous dispersion when it is applied to the surface of theworkpiece, heating the coated surface to a temperature of 350 to 450 F.for half a minute to a minute to dry and set the coating, and curing theresulting thermally set coating by retaining the workpiece at atemperature of 200 to 300 F. for about two hours.

5. A method of preparing continuous lengths of metal strip for coldworking comprising coating the surface thereof with a thermosettingcomposition which consists by weight of the following:

dewaxed shellac 10 to 18 percent glycol 5 to 25 percent of the weight ofdewaxed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellacwater remainder,

the glycol being of the group which consists of hexylene glycol,ethylene glycol, and glycerin, said composition being in the form of anunreac'ted aqueous dispersion when it is applied to the strip surface,heating the coated surface to a temperature of 350 to 450 F. for half aminute to a minute to dry and set the coating, and immediatelythereafter coiling the metal strip and thus retaining the strip at atemperature of 200 to 300 F. for about two hours to cure the coating,the contacting coated surfaces of the strip remaining free of cohesionfor subsequent uncoiling.

6. An reacted aqueous dispersion for coating metal workpieces for coldworking consisting by weight of the following:

dewaxed shellac 10 to 18 percent glycol 5 to 25 percent of the weight ofdewaXed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellacwater remainder,

the glycol being of the group which consists of hexylene glycol,ethylene glycol and glycerin, the shellac and glycol having beendispersed in the water at a temperature of about F. to avoid reactionbetween them, said composition forming a thermosetting coating whenapplied to the surface of a workpiece, dried and heated to a temperatureof 350 to 450 F. for half a minute to a minute.

7. A metal workpiece having on its surface a thermally set coatingformed of a dispersion as defined in claim 6.

References Cited in the file of this patent UNITED STATES PATENTS2,165,056 Kalischer July 4, 1939 2,166,179 Rubin July 18, 1939 2,166,180Rubin July 18, 1939 2,245,100 Bernstein June 10, 1941 2,300,907 BronsonNov. 3, 1942 2,363,540 McVey Nov. 28, 1944 2,365,959 Horwedel Dec. 26,1944 2,386,421 Bassford Oct. 9, 1945 2,387,388 Gardner Oct. 23, 19452,425,023 Bassford Aug. 5, 1947 FOREIGN PATENTS 410,503 Great BritainMay 14, 1934 515,000 Great Britain Nov. 23, 1939 OTHER REFERENCESWarren, Electrical Insulating Materials, 1931, London, pages 138 and418.

1. A METHOD OF COLD WORKING A METAL WORKPIECE COMPRISING CLEANING ANDFINISHING THE SURFACE OF A WORKPIECE, APPLYING TO THE SURFACE A SINGLECOATING WHICH HAS A THICKNESS OF 20 TO 150 MILLIONTHS OF AN INCH AND ISOF A THERMOSETTING COMPOSITION CONSISTING BY WEIGHT OF THE FOLLOWING: